Application of electrical resistivity imaging (ERI) to a tailings dam project for artisanal and small-scale gold mining in Zaruma-Portovelo, Ecuador

• Electrical resistivity imaging (ERI) was applied to a tailings dam project in Ecuador.
• Results showed that the selected site was highly susceptible to landslides.
• Based on such results, an alternative site and a geomorphological conceptual model were proposed.

Thanks to advances in geoelectrical resistivity method over the past two decades, researchers can now gather massive geophysical data sets encompassing long distances and depths, at reasonable cost. The enhanced resolution and spatial coverage of these techniques make them, now, very attractive for use in geological engineering applications, an area for which they were previously charged to be unsuitable. The study shows the capability of electrical resistivity imaging (ERI) to identify key subsoil features that might affect a future tailings dam slated for construction at the Zaruma-Portovelo Mining District, Ecuador. The ERI profiles were gathered and processed with the aim of obtaining resistivity images of a sufficiently resolution for geotechnical use. A geophysical model was created based on these images. The resistivity images were calibrated according to geomorphological, hydrogeological and geotechnical data in order to translate geophysical information into rational geological information. The ERI results, supported by the geomorphological and geotechnical work, suggested that the rock massif is composed of weathering horizons of different rock qualities, slopes are affected by sliding surfaces and these features exert a control on the groundwater flow. These results indicated that the original site selected to construct the dam dike was susceptible to land sliding and an alternative construction site was suggested. Based on the same results, a geomorphological–hydrogeological conceptual model for layered weathered granitic massif in mountainous areas was also proposed.